Revised TSnippetsChkListMgr to use TSortedCollectionCtrlKVMgr to manage association between ISnippet instance and list box text, and also to sort the text: this is instead of having no sorting and using Objects[] array of list box to store TSnippet instances. As a result some method parameter types have changed from TSnippet to ISnippet.
Modified TSnippetsEditorDlg re change of interface to TSnippetsChkListMgr.
